Disposable heat wraps have become a popular way of applying heat to relieve discomfort of temporary or chronic body aches and pains. Disposable heat wraps typically comprise an exothermic composition for generating heat, wherein the exothermic composition typically comprises metal powder, salts, and water that allows the exothermic composition to release heat upon oxidation of the metal powder. Other disposable or reusable devices can use energy produced by neutralization of acids and bases; heat of hydration of inorganic salts; re-heatable gels; and electrical energy to produce heat. Such devices have been found generally suitable for treatment of aches and pains associated with stiff muscles and joints, nerve pain, back pain, rheumatism, respiratory symptoms and the like. Such devices usually produce heat but contain little moisture.
Some disposable heating devices can provide sustained heat for periods of from about one hour to about twenty-four hours, and are generally described as being less messy and more convenient to use than other conventional heat sources such as whirlpools, hot towels, hydrocollators, heating pads and elastic compression bands. However, there are advantages to delivery of both heat and moisture, such as by a whirlpool or hot towel. Moist heat is often felt to be more soothing and comforting, and can deliver heat and pain relief more quickly than dry heat. However, conventional methods of delivering moist heat, such as hot towels and whirlpools, can be cumbersome and inconvenient and are generally not portable. In addition, certain methods, such as hot towels and some current products that claim to deliver steam heat, can only deliver heat for a short period of time, sometimes 15 minutes or less.
Various approaches of enhancing exothermic reactions in portable heat wrap devices to provide longer heating duration and/or provide heat and moisture include the incorporation of various and different carbon materials such as activated and non-activated carbon materials into the exothermic compositions. Other approaches include the addition of water-retainers or water-holding materials to the exothermic composition to allow excess water to be present and water vapor to be generated.
Other approaches to produce heating devices that provide heat and moisture include attempting to regulate the rate and extent of the exothermic reaction, producing water vapor, regulating temperature of the water vapor, and insulating the skin of a user against the potentially skin-damaging temperature of the water vapor. For example, see U.S. Pat. No. 6,629,964 to Ono. However, most known heating methods and devices for providing heat and moisture provide an inadequate amount of water vapor as the known devices either do not produce an amount of water vapor effective to provide sufficient heat and moisture, particularly in deep muscle tissue; or do not produce water vapor for a long period of time, generally for less than about 4 to 8 hours, often for less than an hour, and typically for about 15 minutes. Further, such devices of the prior art are designed to deliver steam or hot vapor per se.
Further the devices of the known art typically generate water vapor by vaporizing water in an exothermic composition. However, it is known that the thermal performance of typical exothermic compositions containing activated carbon and iron are highly sensitive to and dependent on the water level in the composition. Specifically, an excess level of water in an exothermic heat cell can cause a slow rate of heat up. This is due to water restricting the availability of air needed for the exothermic reaction to occur. Thus, the restriction of air results in slow heating and very little or no water vapor generation. However, by trying to reduce the water level in such a composition in order to achieve a fast heat up rate, the duration of the exothermic reaction can be significantly reduced; i.e. the reaction will quickly end because the activated carbon loses its ability to adsorb oxygen as it dries.
In addition, for a high water vaporization rate, an exothermic composition must get quite hot (>65° C.). Moreover, in order to provide deep muscle heating and effective, sustained pain relief in deep muscle, the deep muscle temperature should be above 38° C. However, because human skin can be damaged at elevated skin temperatures believed by those skilled in the art to be above about 43° C., a heating device must be able to keep the skin temperature of a human user below about 43° C. while providing a high amount of heat to the skin and deep muscle. Thus, a moist heat device must protect the skin from the high temperature of an exothermic composition while delivering high levels of heat, by keeping the skin temperature below about 43° C.
Therefore, despite advances in technology for providing heat and moisture, there remains a need for a portable heating device that provides rapid water vapor generation and heat up, provides sustained water vapor generation, delivers an effective amount of heat to provide deep muscle heating, and maintains the skin temperature below about 43° C.